This invention relates generally to structural fasteners for joining various types of materials including composite materials. More specifically, the present invention relates to a pre-coated and sleeved deformable-shank fastener particularly suited for fastening aircraft structural components.
In the aerospace industry today, the use of structural components made from composite materials has become increasingly widespread. The primary method of joining such materials together has been mechanical fastening. Although bonding technology is known and continues to be developed, mechanical joining continues to be the preferred assembly method for structural load-carrying joints, such as the metallic structural components of an aircraft.
When connecting structural aircraft components made from composite materials, great care must be taken not to damage the composite. At the present time, deformable-shank metallic fasteners, such as rivets, are not used to join composite components. This is because during rivet installation and assembly, each end of the rivet is compressed causing outward expansion of the rivet. Such expansion can damage composite sections and result in material fatigue. Therefore, the typical rivet installation and assembly method used, for example, in assembling aluminum aircraft components, will not work with composite structures due to the risk of composite damage caused during rivet installation.
The use of a collar or sleeve surrounding a nut and bolt assembly is known in the fastener field. However, such collars have not been practical in the field due either to the resulting poor fit or the damage caused to the composite material being joined. Further, conventional two-piece fasteners are more expensive to use and are time-consuming to install.
Further, the use of a sleeve, in combination with a rivet, until now, has created more problems in the field than it has solved. Any gaps that occur due to the non-uniform expansion of the sleeve positioned in the hole, or in the rivet within the sleeve can result in a condition known as xe2x80x9cgapping.xe2x80x9d xe2x80x9cGappingxe2x80x9d refers to the creation of gaps, causing discontinuities in the structural assembly. Under high stress forces, gapping can lead to xe2x80x9cfrettingxe2x80x9d, or improper load transfer in the assembled joint, seriously affecting the integrity of the assembly and promoting fatigue. Also, moisture or other residue can collect in the gaps allowing electrical arcing to occur. This can cause, in extreme situations, small explosions that lead to material weakness in the joint resulting in a condition in which the rivet can no longer provide the intended joint integrity. As a result of these and other drawbacks in the current fastener technology, a simple and reliable installation method for metallic fasteners used in fastening or joining composite sections or components is not known.
The present invention relates to fasteners for joining a plurality of components together. In one embodiment, the present invention relates to a fastener for fastening sections of composite material together. The fastener comprises two components. The first component is a sleeve segment that is substantially cylindrical having a predetermined diameter and length. The second component is an core component, preferably solid and coated with a curable organic coating. The core component fits within the substantially cylindrical sleeve component. The sleeve component has an inner diameter slightly greater than the diameter of the core segment. The sleeve component preferably has a length that is less than the length of the core component, and has a wall thickness of from about 0.006 inch to about 0.020 inch.
In a further embodiment, the present invention relates to a fastener for fastening sections of composite material together, wherein the fastener comprises a substantially cylindrical core and a substantially cylindrical sleeve component, one or both of which are coated with a curable organic coating.
In still a further embodiment, the present invention relates to a method for fastening aircraft components together. A plurality of composite aircraft components is provided with each component having a cylindrical opening. The cylindrical openings in the component sections are aligned, and the fastener of the present invention is inserted into the component section openings. The fastener comprises a substantially cylindrical sleeve component, and a substantially cylindrical core component designed to fit within the substantially cylindrical sleeve. The substantially cylindrical core preferably is coated with a phenolic resin containing coating. Pressure is applied to the cylindrical core component deforming the core component and causing the deformed core component to exert substantially uniform radial outward force on the cylindrical sleeve. The sleeve is then deformed in substantially uniform radially outward directions to positively secure the composite sections.
Still further, an embodiment of the present invention is directed to aircraft comprising composite parts held together with two-component fasteners that comprise a coated core component that fits within a sleeve component. One or both of the core and sleeve components preferably are coated with a curable organic coating.